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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
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NASA NTRS1980

Observations of electron gyroharmonic waves and the structure of the Io torus

Narrow-banded emissions were observed by the Planetary Radio Astronomy experiment on the Voyager 1 spacecraft as it traversed the Io plasma torus. These waves occur between harmonics of the electron gyrofrequency and are the Jovian analogue of electrostatic emissions observed and theoretically studied for the terrestrial magnetosphere. The observed frequencies always include the component near the upper hybrid resonant frequency, (fuhr) but the distribution of the other observed emissions varies in a systematic way with position in the torus. A refined model of the electron density variation, based on identification of the fuhr line, is included. Spectra of the observed waves are analyzed in terms of the linear instability of an electron distribution function consisting of isotropic cold electrons and hot losscone electrons. The positioning of the observed auxiliary harmonics with respect to fuhr is shown to be an indicator of the cold to hot temperature ratio. It is concluded that this ratio increases systematically by an overall factor of perhaps 4 or 5 between the inner and outer portions of the torus.

Birmingham, T. J.↗
NASA NTRS1980

Mass-loading and diffusion-loss rates of the Io plasma torus

Limits to the mass-loading and diffusion-loss rates of ions in the Io plasma torus have been calculated on the assumption that observed optical emissions are controlled by electron-ion collisions. Calculations of the yield of emission from the vicinity of Io limit the mass-loading rate to the order of 10 to the 27th per s for S II or O II, on the grounds that electron-excited emissions associated with the location of Io have not been observed in the optical spectrum. This mass-loading limit is dependent on the assumptions that Io is the source of torus particles and that most of the neutral atoms are converted to ions within 1 R(J) of Io. According to the calculations presented below, the observed partitioning of sulfur ion species in the hot torus at the time of Voyager 1 encounter indicates that the diffusion-loss time of the ions is of the order of 1/D = 100 days. The two results limiting the mass-loading and diffusion-loss rates are compatible and suggest that the energy required to maintain the observed radiated power cannot be supplied by acceleration of ions formed at Io in Jupiter's rotating magnetic field.

Shemansky, D. E.↗
NASA NTRS1982

The injection of energy into the Io plasma torus

Voyager EUV observations of the Io plasma torus indicate the presence of an intensity modulation in the corotating reference frame of significant magnitude on a 10-hour time scale. The phenomenon has a persistence which suggests it is a permanent feature, and the magnitude is such that a substantial amount of energy is injected into the torus at a 10-hour periodic rate. An investigation is conducted regarding the nature of the energy enjection process as determined by the plasma parameters and the observed characteristics. Attention is given to excitation-relaxation relations, aspects of ion-electron relaxation, and electron-electron relaxation and energy transfer rates. The radial distribution of temperature at the eastern and western elongations is found to indicate that the energy input to the electrons is distributed over the width of the torus. The dominant mechanism of energy transport to the plasma appears to be electron-electron heating.

Shemansky, D. E.↗
NASA NTRS1982

On the structure of the Io Torus

Since the plasma flow near Io is reduced, neutrals originating in charge exchange are not energetic enough to leave the Jovian system and are therefore distributed over an extensive region, as indicated by the sodium cloud. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field, and the radial current driven by the pickup process cannot close in the Io torus, so that it must instead be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud, and towards it at the inner edge. It is found that the Jovian ionospheric photoelectrons also cannot supply the current flowing away from the equator, so that torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is large enough to push the torus into the Jovian atmosphere, explaining both the sharp, discontinuous change of flux tube content and ion temperature at L equals 5.6, as well as the generation of Auroral-type hiss at that point.

Goertz, C. K.↗
NASA NTRS1983

Experimental and finite element study of a standing torus under normal and tangential loads

The effect of a combined external load consisting of a normal component and a tangential braking force applied to an inflated torus is addressed. Experimental results obtained by photographic study of the contact area between the torus and load plate are presented as well as measurements of the vertical and horizontal displacement of the torus under load. A numerical procedure for displacement analysis is developed in which the finite element program STAGS (Structural Analysis of General Shells) is used in an iterative manner to produce a flat, horizontal footprint surface under force loading. The redistributed force distribution obtained by the iterative process is displayed along with computed meridional and circumferential stresses. Finally, an extension of the iterative method is introduced which eliminates the need to experimentally determine the footprint area.

Flugrad, D. R.↗
NASA NTRS1982

On the nature of S II emission from Jupiter's hot plasma torus

An effective electron temperature T(e) of 80,000 K is indicated by the Voyager 1 encounter Jupiter hot torus emission rates in the 6731, 1256, 911 and reclassified 765 A transitions of S II. A set of 53 measurements of the S II red line doublet obtained at 5.9 Jupiter radii shows strong, irregular fluctuations in intensity, but no variation in the line ratio. At this distance from Jupiter, the torus is found to be longitudinally uniform in density; this is consonant with Voyager UVS findings, but contrary to magnetic anomaly model predictions. It is suggested that presently unidentified ion-ion and/or iron-atom reactions are responsible for the S II component irregular variations, in view of the fact that electron properties are regular and variable only over a small range in the hot torus at 5.9 Jupiter radii.

Brown, R. A.↗
NASA NTRS1982

In situ observations of Io torus plasma

The physical properties of the Io plasma formation deduced from in situ observations are described. The torus plasma is characterized by spatially distinct regions with steep gradients in plasma parameters between them. The innermost region has a cool plasma which collapses toward the centrifugal equator and gives rise to a distinctive localized concentration of plasma well inside of Io's orbit. The next region has a warm plasma which includes the L-shell of Io and is the presumed injection region of the plasma. Other regions, known as the plasma ledge and ramp, are described. The changes in plasma characteristics are accounted for by centrifugally driven flux tube interchange diffusion to provide radial mass transport. The ramp is shown to result from impoundment of the plasma by the inner edge of the energetic particle population. It is also shown how the power required to excite the ultraviolet emissions of the torus and the Jovian aurora determines the rate at which new plasma is fed into the torus.

Sullivan, J. D.↗
NASA NTRS1983

The problem of cooling the cold Io torus

Two models are developed for the transport of ions inward from Io's orbit, the first using the assumption that radial diffusion is the dominant transport mechanism while the second uses a combination of diffusive and convective transport. The models include thermal and number density transport, radiation, ionization and pickup of local neutrals, recombination, charge exchange, and Coulomb interactions. It is found that pure diffusive transport can account for the dramatic inward depletion of the torus only by invoking recombination or by postulating a massive increase in the production rate of torus ions sometime prior to the Voyager mission. Recombination is determined to be far too slow to be the cause of the observed density decrease inside of Io. The model combining convection and diffusion is shown to reasonably match the data, but only if a diffusion coefficient 100 times less than that derived from Pioneer observations is used. In addition, it is shown that the Pioneer derived diffusion rate combined with Voyager temperature and density measurements indicate a large nonradiative sink of energy in the inner torus.

Richardson, J. D.↗
NASA NTRS1983

Spectrophotometric studies of the Io Torus

A toroidal volume near Io's orbit is made luminous by multiple optical and ultraviolet line emissions excited by resonant scattering of sunlight and by electron collisions. These emitting atoms and ions have been lost from Io. The spectrophotometric measurements of these emissions and their physical interpretation are considered. It is now known that the flow of material from Io dominates the particle and energy budgets of the Jovian magnetosphere. The observed emitting species in the Io torus are examined, and the atomic clouds are discussed, taking into account morphology and kinematics, atomic cloud supply rates, ion-atom collisions, and charge-exchange collisions. Observations and studies concerning the plasma torus are reported, giving attention to the forbidden lines, the extreme ultraviolet lines, and aspects of ion temperature and spatial distribution. Two types of radial transport in the Io torus include the ballistic motion of neutrals escaping from Io and the cross-L transport of ions.

Brown, R. A.↗
NASA NTRS1985

Ion partitioning in the hot Io torus - The influence of S2 outgassing

An alternative time-independent model of the ion partitioning in the hot Io torus is proposed which introduces the ratio of sulfur to oxygen in the neutral source as a free parameter. Measurements of the ion abundances in the torus plasma are presented and discussed, noting some ambiguities and identifying the features that are well established. Physical processes important to the understanding of the ion partitioning calculation are reviewed. The results of the model are discussed in the context of observational constraints, and spectroscopic constraints are discussed. It is concluded that a bimodal source model, together with a small percentage of hot electrons and a relatively short diffusion time scale, can account for the principal observational features without invoking significant time variability. In particular, the O III deficiency observed in 1981 can be obtained in a model that produces other aspects of the torus ion partitioning measured during the Voyager 1 encounter.

Moreno, M. A.↗
NASA NTRS1986

The Io sulfur torus in 1981

A Fabry-Perot spectrometer was used to obtain images of the Io torus in emission lines of S II (wavelength 6716 and 6731) and S III (wavelength 9531) in February and March 1981, on the 2.1 meter telescope at KPNO. The S II and S III images showed a large variation in brightness and radial extent. There is an indication the S II and S III emissions in the warm torus are correlated. The S II and S III emissions in the warm torus also have similar scale heights along the magnetic field lines of approximately 0.6 to 0.72 R sub J. The east-west asymmetry in the S II images taken at similar magnetic longitudes, but 2.5 Jovian rotations apart, supports the theory of convective motions suggested by others. In addition to the images, simultaneous measurements of the S II (6731 wavelength) line profile were also made on one night using a Fabry-Perot scanning spectrometer on the 4 meter at KPNO. The S II spectral scans implied ion temperatures of 52 (+ or - 10) x 10 to the 3rd at 5.2 to 5.6 R sub J from Jupiter and a minimum temperature of at least 3 x 10 to the 5th K at 6 R sub J from Jupiter.

Oliversen, Ronald J.↗
NASA NTRS1988

A comprehensive model of ion diffusion and charge exchange in the cold Io torus

A comprehensive analytic model of radial diffusion in the cold Io torus is developed. The model involves a generalized molecular cloud theory of SO2 and its dissociation fragments SO, O2, S, and O, which are formed at a relatively large rate by solar UV photodissociation of SO2. The key component of the new theory is SO, which can react with S(+) through a near-resonant charge exchange process that is exothermic. This provides a mechanism for the rapid depletion of singly ionized sulfur in the cold torus and can account for the large decrease in the total flux tube content inward of Io's orbit. The model is used to demonstrate quantitatively the effects of radial diffusion in a charge exchange environment that acts as a combined source and sink for ions in various charge states. A detailed quantitative explanation for the O(2+) component of the cold torus is given, and insight is derived into the workings of the so-called plasma 'ribbon'.

Barbosa, D. D.↗
NASA NTRS1989

Near-infrared morphology of protoplanetary nebulae - The icy dust torus of Minkowski's Footprint (M1-92)

High-resolution near-infrared images and ice-band spectra of the protoplanetary nebula M1-92 (Minkowski's Footprint) are presented. The direct images of the object display a typical bipolar morphology with the star located in the center of the nebula illuminating two lobes. The overall dimensions are the same in the J, H, and K infrared bands, and they are similar to those in the optical range. The near-infrared color images clearly reveal a dust torus around the central star. The orientation of the object in the plane of the sky allows the simultaneous view of the illuminating star, the nebular lobes, and the dust torus in a highly favorable perspective, only rarely found in other bipolar nebulae. The ice-band spectra make it possible to locate the H2O-ice grains within the dust torus; in addition, the narrow ice feature indicates that the ices are primarily pure crystalline water.

Eiroa, C.↗
NASA NTRS1992

System III variations in apparent distance of Io plasma torus from Jupiter

System III variations in apparent distance of the Io plasma torus from Jupiter are examined on the basis of data obtained from UVS scans across Jupiter's satellite system. The displacement of the dawn and dusk ansae are found to be unexpectedly complex. The displacements are unequal and both ansae are in motion with the motion of the approaching ansa being the lesser of the two. The radial motions, as measured from either the center of Jupiter or the offset-tilted dipole, are of unequal magnitude and have the System III periodicity. It is concluded that the cross-tail electric field that causes these torus motions is concentrated on the dusk ansa, varied with the System III period, and shows magnetic-anomaly phase control. It is found that the dawn-dust asymmetry in brightness is not explained simply by the cross-tail electric field. It is concluded that there is a heating mechanism that causes the dusk side of the Io plasma torus to be brighter than the dawn side.

Dessler, A. J.↗
NASA NTRS1994

Periodic intensity variations in sulfur emissions from the Io plasma torus

In November and December 1988, we acquired 157 spectra of (S II) lambda 6731 emissions from the Io plasma torus with a Fabry-Perot interferometer at the McMath-Pierce Solar Telescope facility on Kitt Peak. A major goal of this experiment was to extend our earlier studies of intensity variations in the plasma torus. Our earlier analysis (F. L. Roesler, F. Scherb, and R. J. Oliversen, 1984, of (S III) lambda 9531 emission spectra acquired in April 1982 had shown that the intensity of torus emissions varied periodically with a period of 10.20 +/- 0.06 hr (1-sigma uncertainty level), slightly longer than Jupiter's System 3 rotational period of 9.925 hr. We present here an reanalysis of our 1982 data revealing, in addition to the 10.20-hr period, a clear secondary periodicity at 9.95 +/- 0.906 hr. By constrast, we show that our new (S II) lambda 6731 data have a single period of 10.14 +/- 0.03 hr. which is neither the System 3 period nor the proposed 'System 4' period of 10.224 hr.

Woodward, R. Carey, Jr.↗
NASA NTRS1995

Rocket FUV Observations of the Io Plasma Torus During the Shoemaker-Levy/9 Impacts

We observed the Io torus from 820-1140 A on universal time (UT) 20.25 July 1994 from a sounding rocket telescope/spectrograph. These observations serve as only the fourth published spectrum of the torus in this wavelength range, and the only far ultraviolet (FUV) data documenting the state of the torus during the Shoemaker Levy 9 Impacts.

Stern, S. A.↗
NASA NTRS2004

Modeling Temporal Variability of Plasma Conditions in the Io Torus during the Cassini Era

Observations of ultraviolet (UV) emissions from the major ion species (S(sup +), S(sup ++), S(sup +++), O(sup +), O(sup ++) of the Io Plasma torus made during the Cassini flyby (October 2000 to March 2001) have revealed significant time variability. Using a homogenoeus model for mass and energy flow in the torus parameterized by five input variables (transport timescale, neutral source strength, ratio of oxygen to sulfur atoms in the source, fraction of superthermal electrons, and temperature of the hot electrons), we have investigated the time variability of the torus properties (density, composition, and temperature) during the Cassini era. In order to match the changes in emissions, the model suggests that a significant change in the neutral source occurred near the beginning of the observing period, decreasing from more than 1.8 tons/s to 0.7 tons/s. The changes in the neutral source appear to coincide with the declining phase of a dramatic (i.e., 2-3 order of magnitude) peak in iogenic dust emissions observed by Galileo prior to the Cassini era.

Delamere, P. A.↗
NASA NTRS2008

An Axisymmetric Hydrodynamical Model for the Torus Wind in AGN: X-ray Excited Funnel Flow - 2

We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields, mass fluxes and temperature, as functions of the torus properties and X-ray flux. Synthetic warm absorber spectra are calculated, assuming pure absorption, for sample models at various inclination angles and observing times. We show that these models have mass fluxes and flow speeds which are comparable to those which have been inferred from observations of Seyfert 1 warm absorbers, and that they can produce rich absorption line spectra.

Dorodnitsyn, A.↗